The commercial development of hydrocarbon (e.g., oil and natural gas) fields requires significant capital investment. Thus it is generally desirable to have as much information as possible pertaining to the contents of a hydrocarbon reservoir and/or geological formation in order to determine its commercial viability. There have been significant advances in measurement while drilling and logging while drilling technology in recent years (hereafter referred to as MWD and LWD, respectively). These advances have improved the quality of data received from downhole sensors regarding subsurface formations. It is nonetheless still desirable to obtain one or more formation fluid samples during the drilling and completion of an oil and/or gas well. Once retrieved at the surface, these samples typically undergo specialized chemical and physical analysis to determine the type and quality of the hydrocarbons contained therein. In general, it is desirable to collect the samples as early as possible in the life of the well to minimize contamination of the native hydrocarbons by drilling damage.
As is well known to those of ordinary skill in the art, formation fluids (e.g., water, oil, and gas) are found in geological formations at relatively high temperatures and pressures (as compared to ambient conditions at the surface). At these relatively high temperatures and pressures, the formation fluid is typically a single-phase fluid, with the gaseous components being dissolved in the liquid. A reduction in pressure (such as may occur by exposing the formation fluid to ambient conditions at the surface) typically results in the separation of the gaseous and liquid components. Cooling of the formation fluid towards such ambient temperatures typically results in a reduction in volume (and therefore a reduction in pressure if the fluid is housed in a sealed container), which also tends to result in a separation of the gaseous and liquid components. Cooling of the formation fluid may also result in substantially irreversible precipitation and/or separation of other compounds previously dissolved therein. Thus it is generally desirable for a sampling apparatus to be capable of substantially preserving the temperature and/or pressure of the formation fluid in its pristine formation condition.
Berger et al., in U.S. Pat. No. 5,803,186, disclose an apparatus and method for obtaining samples of formation fluid using a work string designed for performing other downhole work such as drilling, workover operations, or re-entry operations. The apparatus includes sensors for sensing downhole conditions while using a work string that permits working fluid properties to be adjusted without withdrawing the work string from the well bore. The apparatus also includes a relatively small integral sample chamber coupled to multiple input and output valves for collecting and housing a formation fluid sample.
Schultz et al., in U.S. Pat. No. 6,236,620, disclose an apparatus and method for drilling, logging, and testing a subsurface formation without removing the drill string from the well bore. The apparatus includes a surge chamber and surge chamber receptacle for use in sampling formation fluids. The surge chamber is lowered through the drill string into engagement with the surge chamber receptacle, receives a sample of formation fluid, and then is retrieved to the surface. Repeated sampling may be accomplished without removing the drill string by removing the surge chamber, evacuating it, and then lowering it back into the well. While the Berger and Schultz apparatuses apparently permit samples to be collected relatively early in the life of a well, without retrieval of the drill string, they include no capability of preserving the temperature and/or pressure of the formation fluid. Further, it is a relatively complex operation to remove the formation fluid sample from the Berger apparatus.
Michaels et al., in U.S. Pat. Nos. 5,303,775 and 5,377,755, disclose a Method and Apparatus for Acquiring and Processing Subsurface Samples of Connate Fluid in which one or more fluid sample tanks are pressure balanced with respect to the well bore at formation level (hydrostatic pressure). The sample tank(s) are filled with a connate fluid sample in such a manner that during filling thereof the pressure of the connate fluid is apparently maintained within a predetermined range above the bubble point of the fluid. Massie et al., in U.S. Pat. No. 5,337,822, disclose a Well Fluid Sampling Tool for retrieving single-phase hydrocarbon samples from deep wells in which a sample is pressurized by a hydraulically driven floating piston powered by high-pressure gas acting on another floating piston. One drawback of the Michaels and Massie apparatuses is that they require prior withdrawal of the drill string before they can be lowered into the well bore, which typically involves significant cost and time, and increases the risk of subsurface damage to the formation of interest.
Therefore, there exists a need for improved apparatuses and methods for obtaining samples of formation fluid from a well. In particular, there exists a need for an apparatus that does not require retrieval of the drill string from the well and that has the capability of preserving the sample of formation fluid in substantially pristine condition.